The Aasee is a large artificial lake southwest of the old town, created in 1927 by damming the Aa river. It is Münster's main outdoor recreation area: a 5-kilometre loop around the lake is popular with joggers, cyclists, and families, and in summer the lakeside fills with students from the university nearby. Pedalos and rowing boats can be hired on the lake's western shore.
The Allwetterzoo (all-weather zoo) sits on the lake's north bank — a competent mid-sized zoo with particular strength in its dolphinarium and a walk-through butterfly house. The associated Westfälisches Pferdemuseum (Horse Museum) is an unusual institution covering the history and culture of horses in Westphalia, housed in an old city house. Both are popular with families. The Aasee is about 20 minutes' cycle from the cathedral.